High or low voltage detector



Jan. 16, 1945. c. s. KNOWLTON HIGH OR LOW VOLTAGE DETECTOR Filed Feb.20,

LJ PHASE CIRCUIT J F/G. Z

NVWENTOR S. KNQWLTO/V ATTORNEY Patented Jan. 16, 1945 HIGH OR LOWVOLTAGE DETECTOR Clarence S. Knowlton, Springfield, N. J., assignor toBell Telephone Laboratories, Incorporated, New York, N. Y., acorporation of New York Application February 20, 1943, Serial No.476,598

2 Claims.

This invention relates to an improved and simplified arrangement fordetecting abnormal conditions in polyphase alternating current circuitssuch, for example, as a high or low voltage condition, but not both, ora reversal of phase rotation, and more particularly to the use of asingle, or common, three-element gas-filled discharge device fordetecting such abnormal conditions in two or three-phase transmissionlines.

The use of a three-element gaseous device for detecting either a high ora low voltage condition in a single phase transmission line is old asshown for example in applicants Patent 2,197,868, issued April 2-3,1940, and it is obvious that were it desired to detect such conditionsin more than one phase of a polyphase circuit, it would only benecessary to duplicate the arrangement of the patent for each phase tobe monitored.

A feature of the present invention, however, re-

sides in the use of a single three-element gasfilled discharge devicehaving its control and main discharge circuits individually connectedacross different Ones of said phases, and so adjusting thecharacteristic of said device and its connection to the phases that apredetermined potential across the phase to which the control circuit isconnected will cause ionization of the device for an interval sufficientto permit a discharge to be established between the anode and cathodewhen the potential across the phase to which the main discharge circuitis connected also reaches a predetermined value thereby permitting theper,- formance of any desired circuit function such as actuating a relayto control a signal device which may indicate a low voltage in eitherphase by its failure to operate.

Alternatively, a high voltage condition can be detected by employing agas-filled device whose control gap will only discharge to causeionization at above normal potential. When used as a high voltage alarmthe control gap will break down only at higher than normal voltage inthe phase to which it is connected, thus ionizing the device whereuponthe main gap will fire to operate a relay and give an alarm.

It is, of course, understood that any voltage unbalance in one phase ofa three-phasecircuit will be reflected in the other two phasessuflicient to affect ionization and discharge of the device connectedthereto.

Further, if it is assumed that a reversal of rotation occurs between anytwo of the phases of a three-phase circuit if the discharge device has arelatively short deionizing time and the main gap potential applied tothe anode, ionization due to the control gap breakdown will cease beforethe potential on the anode has risen to a suflicient value to maintainthe discharge across the main gap and therefore the signal relay willrelease to indicate an abnormal condition.

The invention will be understood from the following description whenread in connection with the accompanying drawing:

Fig. 1 of which shows a three-phase transmission line to which isconnected means in accordance with the invention for indicating a lowvoltage condition in any one of the three phases which it will beunderstood are 120 degrees apart;

Fig. 2 shows the relation of the voltages of three phases which it isdesired to monitor; and

Fig. 3 shows the relation of the voltages of a two-phase circuit. 2

Referring to Fig. 1 of the drawing two transformers T1 and T2 areconnected open delta to a three-phase line L and the cathode k of thecold cathode gas-filled device I is connected to the common point of thetwo secondary windings. The control anode c is connected by means ofpotentiometer T to the free terminal of the secondary winding oftransformer T1 and the main anode a is connected in series with a relay2 to the free terminal of the secondary of transformer T2. A condenser 3is connected in shunt to relay 2 for the purpose of preventing the relayfrom releasing between successive pulsations of current applied thereto.The transformation ratios of the transformers Ti and T2 and the settingof the slider of potentiometer P are such that the control gap kc of thedevice1wi1l break down near the peak of the normal line voltage in phaseC and the main gap ak of the device will fire a short interval afterionization occurs. For example by referring to Fig. 2,which shows therelation of the three phases A, B and C, it will be noted that whenphase C approaches its negative peak voltage vc, the control gap willfire as shown by the shaded area cz'-, thus ionizing the device and thatalmost immediately thereafter the potential of phase B reaches. a pointob iwhich is high enough to permit the main gap of the device I to firethus operating relay 2, there'- by opening the circuit of the pilot lamp4. Condenser 3 charges in parallel with relay 2 and when the voltage ofphase B drops below the sustaining voltage of the main gap, thusstopping the discharge, the condenser 3 will discharge through therelaythus holding it operated until the main gap is again fired on thenext cycle.

It will be obvious from the foregoing that if the voltage of eitherphase C or B falls below its normal value, relay 2 will release thusclosing the circuit of lamp 4.

As stated previously it the voltage of phase A drops below its normalvalue, it will reflect an unbalanced condition in phases C and B thuspreventing device I from operating and permitting the relay to release.

If the device I is polarized, that is, its main discharge path conductsin only one direction (anode-cathode) relay 2 will be energized onceeach cycle, i. e., when phase C approaches the peak of its negative halfwave and phase B approaches its positive peak whereas if the device I isnot polarized, that is, will discharge in either direction, then relay 2will be energized twice each cycle, once when the phase C reaches itsnegative peak and phase B is approaching its positive peak and againwhen phase C reaches its positive peak and phase B is approaching itsnegative peak.

Obviously, if a phase reversal occurs in the line and the voltageapplied to the control electrode C of device I is derived from phase A,instead of phase C, the periods when the device will be ionized will berepresented by the unshaded portion ai+ and aiand if the device has ashort deionizing time, deionization will be completed and the devicerestored to normal before there is suflicient voltage in phase B toinitiate and maintain an arc. This provides a check circuit sensitive tophase rotation and relay 2 will be released and lamp 4 lighted in casesuch a reversal occurs. If, however, the device I is so constructed asto have a relatively long deionizing time, which is sufiicient to holdover until the voltage of phase B approache its peak value, then relay 2will hold operated regardless of whether the control electrode isconnected to phase C or A.

It will be understood that byemploying a discharge device having arelatively long deionizing time the foregoing arrangement, shown in Fig.1, as connected to a three-phase system, can be adapted for use on atwo-phase circuit the relation between the phases of which is shown inFig. 3, that is if the control gap is connected to phase X, and the maingap to phase Y, ionization of the device occurs near the peaks of phaseX and the main gap will fire as the voltage of phase Y approaches itspositive peak, i. e., once per cycle and if the device is non-polarizedit will fire twice per cycle, that is when the voltage approaches boththe positive and negative peaks.

If the foregoing arrangement is employed as a high voltage alarm, thenit is only necessary to adjust the circuit elements in such a mannerthat the control and main gaps of the device I will not fire until apredetermined higher than normal potential is reached and to connectlamp 4 in such a manner that it will be lighted when relay 2 is operatedinstead of released.

What is claimed is:

1. In a system for detecting a non-standard condition in polyphasetransmission lines, a gasfilled discharge device having an anode, acathode, a control electrode and an output circuit, circuit means forconnecting said control electrode and cathode to a first phase of saidline, and other circuit means for connecting the anode and cathode inseries with said output circuit to a second phase, said device being soconstructed and said circuits being so adjusted and arranged that thedevice will ionize when the voltage of the phase to which the controlelectrode is connected reaches a predetermined value and will remainionized until the voltage applied to the anode from the second phasereaches another predetermined value whereupon a glow discharge will beestablished between said anode and cathode, and means for indicating thefailure of said device to establish a glow discharge during a cycle ofsaid alternating current.

2. A three-phase supply circuit, a gas-filled discharge device having ananode, a cathode, and

a control electrode, circuit means for connecting said cathode andcontrol electrode to a first phase and the cathode and anode to a secondphase, said device being so constructed and said circuits being soadjusted and arranged that the device will ionize when the voltage ofthe phase to which 40 the control electrode is connected reaches a pre-

